Method and apparatus for enhanced pathogen mortality in ventilation systems using solid state means of generation of uvc

ABSTRACT

A novel method and apparatus is presented wherein an output of infra-red solid state laser or multiple of such lasers is quadrupled in frequency to obtain a laser output that emits energy in ultra violet C spectrum, and wherein this energy is then provided within an air duct as is normal in HVAC systems so as it kill pathogens that are airborne and being carried through the conduit. Further such a method reduces production of ozone, detrimental to human health and produced in other means of generating UVC and provides ease of control of such energy so as to maintain the required energy at a steady level for prolonged period of time.

TECHNICAL FIELD

The present application relates to ventilation systems. The presentapplication also relates to pathogen control using UVC.

BACKGROUND

The knowledge that electromagnetic radiation with wavelengths in theUltra Violet C band (210 nm to 280 nm) kills bacteria is wellestablished with the first recognition of this discovery resulting in aNobel prize awarded to Niels Ryberg Finsen for Physiology or Medicine in1903. It is now known that DNA of living organisms is highly absorbentat 260 nm.

Pathogens are a serious issue in hospitals, killing over 100,000 personsper year in the USA. Pathogens are spread from infected individualsthrough touch and through the air. Removal of pathogens is verydifficult. Filtration is commonly used but does not remove the pathogen;filtration makes matters worse by providing sites for the pathogens tomultiply as filtration does not kill them. UVC using mercury andfluorescent lamps have been used but cost, production of ozone,maintenance and heat are barriers to large scale adoption.

Life on this planet evolved in the absence of UVC, specifically 260 nmwavelength of light. The ozone layers shields the planet form thiswavelength of electro-magnetic radiation. All life forms are extremelysensitive to this wavelength and cells are destroyed with small doses ofthis radiation. In simple organisms, this means immediate death, incomplex organisms, it means various cancers and cellular destructionleading to death.

The first attempts in removing pathogens from the air were to filterthem out as disclosed by M. WILEY et al in U.S. Pat. No. 3,347,025.Filters at that time were not fine enough to be helpful as well as thepathogens were not killed. Filters do block bacteria but not allpathogens as well as the filter surfaces become sites for the pathogensto grow in numbers.

Attempts with varying levels of success have been made to use UVC tokill pathogens to date.

Traditionally UVC is created through the mercury arc lamps and throughgas discharge tubes. These sources produce a complex spectrum ofelectromagnetic radiation and some of it is in the UVC region and asmaller part of this UVC is exactly in the region that is of interest inkilling pathogens.

The production of UVC by above means also produces ozone as a sideeffect of the use of high strength electromagnetic field necessary tooperate the lamps. In this application ozone has to be removed as it ishas a negative impact on human health. This adds to the cost and thecomplexity of the equipment.

An alternative method of removing pathogens from the air is to use HEPAfilters as disclosed by Mark A. Tuckerman et al in U.S. Pat. No.5,616,172. This method has a draw back as the pathogens are not killedbut blocked and the filter surfaces are used by the pathogen tomultiply. Periodic replacement of the filters can solve this but at acost of very frequent maintenance. Smaller pathogens, like viruses,cannot be removed by this method.

Further improvement on this filter based method has been disclosed byWilliam Morrow et al in U.S. Pat. No. 5,656,242, where UVC produced fromtube lights is used to kill the pathogen that is deposited on the filtersurfaces. Although an improvement, the method requires a large number oftube lights, regular replacement of these tube lights as they haverapidly declining power curve with time and they need to be operatingtwenty four hours a day and very day.

Another method found in U.S. Pat. No. 7,407,633 uses UV light to createozone to kill pathogens. While effective in killing most forms ofbacteria, ozone still needs to be removed.

US Pre-Grant Patent Application Publication (PG-Pub) 2005/0249630 A1 byOlubunmi Ayodele Odumuye et al discloses a method wherein UV lightproduced by tube lights is used to purify the air or other carriers ofpathogens such as water. This method suffers from the drawbacks of allof the above methods, namely it is costly and produces ozone.

US PG-Pub 2010/0320440 A1 teaches producing electromagnetic radiation inUVC, specifically 365 nm, aimed at killing pathogens. This method iseffective provided there is sufficient time to overcome the low power ofthese devices and is confined to purifying water in small containersover hours.

In U.S. Pat. No. 6,555,011 by Zamir Tribelsky et al, claim is made of anapparatus whereby the gas or liquid to be disinfected is contained in aparabolic chamber that is then exposed to electromagnetic radiation ofmany types, the claim is broad without specific information on how toimplement such a solution using lasers and claim is confined to use in aparabolic chamber.

US PG-Pub 2011/0142725 A1 by Xuanbin Liu et al discloses an airpurification method that uses electromagnetic radiation through a glasswith a coating of a photo catalyst and the light source claim limited toVCSEL, led, lamps but not solid state lasers.

SUMMARY

A novel method and apparatus is presented wherein an output of infra-redsolid state laser or multiple of such lasers is quadrupled in frequencyto obtain a laser output that emits energy in ultra violet C spectrum,and wherein this energy is then provided within an air duct as is normalin HVAC systems so as it kill pathogens that are airborne and beingcarried through the conduit. Further such a method reduces production ofozone, detrimental to human health and produced in other means ofgenerating UVC and provides ease of control of such energy so as tomaintain the required energy at a steady level for prolonged period oftime.

The invention disclosed here and considered to be a preferred embodimentand which must be read as one particular implementation of thisdisclosure, without limitation of other embodiments, comprises an IRlaser diode or diodes, emitting radiation at 1040 nm coupled to a solidstate frequency doubler comprising a crystal and two mirrors, the outputof which is 520 nm and a second frequency doubler comprising a crystaland two mirrors, the output of which is 260 nm. As the output needs notbe a collimated beam, the crystals can be of poorer quality, thusreducing costs.

The output radiation is allowed to expand with a large angle ofdivergence against the normal practice of the art to have a highlycollimated output.

It is clear to those familiar with the art that almost no ozone iscreated as there is no high level electromagnetic field present.

The radiation generating system is coupled to a detector that is thenfed back to form a feedback loop that controls the output power andkeeps it constant, increasing the current as the crystals age over time.

The whole apparatus is then contained inside of an HVAC conduit throughwhich the medium to be treated passes. The insides of the conduit arecovered with a reflective material such that the radiation reflects ofthe wall multiple times prior to being absorbed.

Multiple units may be used in a single HVAC conduit depending on theneeds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a two-stage quadruple harmonic generation ofUVC from an IR source.

FIG. 2 shows a HVAC duct with two UVC Radiation Generators on each sideof the duct. A cut out of the duct shows one of the opening throughwhich the UVC radiation enters the duct. The air moves longitudinallythrough the duct.

FIG. 3 shows how the radiation from the two UVC Radiation Generatorsfills the duct. The inner surfaces of the duct are coated with a UVCreflective material. The radiation reflects multiple times so as to fillthe duct.

DETAILED DESCRIPTION

A preferred embodiment of this disclosure is presented here withoutlimitation to other forms of implementing the solution described in thedisclosure. These forms may vary the number of UVC Radiation Generatorsor their orientation.

A means of generating UVC through two stage frequency doubling isdisclosed and will be well understood by persons with knowledge of thediscipline. Standard methods of frequency doubling desire to produce asource of electromagnetic radiation that is collimated, thus requiringhigh quality optical components specifically the crystals that need tobe without structural defects in the crystal lattice. These means incura high cost. This unit in this disclosure that generates the UVCradiation is referred to as the UVC Radiation Generator.

This disclosure and the intent does not require collimated radiation, itrequires the radiation to spread as wide as possible as the radiationneeds to spread to cover the volume of the air duct in which theradiation source needs to be installed as further disclosed below.Therefore it will be understood that the lack of collimation means thatthe crystals do not have to be perfect and the optics can be chosen sothat the cost is lower.

FIG. 1 shows an IR laser diode (LD) 1 acting as a pumping source andhaving an output beam directed to a mirror 2 positioned at an angle tothe beam and that is highly reflective for the fundamental beam andtransparent for the pumping beam. The beam from the IR laser diode 1passes through the mirror 2 into a laser medium 3. The laser medium 3can comprise Nd:YAG, Nd:YLF, Nd:YVO₄, Ti:Sapphire or other lasermediums, and operates at 1040 nm. The light passing through the lasermedium 3 passes through a Q switch 4 and strikes mirror 5 that is highlyreflective for the fundamental beam. The beam leaving laser medium 3that strikes mirror 2 is reflected to a mirror 6 that is transparent forthe fundamental beam and highly reflective to the harmonic beamgenerated in a first nonlinear medium, harmonic generation crystal 7 anda second nonlinear medium, harmonic generation crystal 8. Light leavingcrystal 8 passes through a mirror 9, shaping optics 10 (lenses, mirrorsor prisms), and an optical delay prism 11. Light at 520 nm leavesoptical delay 11 passes through shaping optics, lenses, mirrors orprisms 12 into a third nonlinear medium, harmonic generation crystal 13,and exits to a mirror 14. Light passing through mirror 14 and an outputdevice 15 that transmits a fourth harmonic beam is at a wavelength of260 nm.

In the preferred embodiment, two such UVC Radiation Generators areinstalled in an HVAC conduit in opposition to each other, as is shown inFIG. 2, as well as the inner surface of the conduit are coated with acoating that is highly reflective of UVC radiation (FIG. 3). Theresulting combination of the radiation pattern from the two UVCRadiation generators and the reflection from the inner surfaces of theHVAC duct provides sufficient energy in the duct so substantially allthe pathogens being carried in the air are subject to 260 nm radiation.The resulting radiation in the duct is shown in FIG. 3.

There will be other arrangements wherein the number of UVC RadiationGenerator may be more or less than two and may be placed in any othergeometry as may be relevant to the desired level of energy exposurerequired.

Each of the two radiation sources has a sensor sensitive to UVC that isconnected to a feedback control electronic circuit that controls thepower of the excitation source in the UVC generator. Thus the radiationenergy density is maintained through the operating life of the systemand the elimination of the pathogens is predictable. This ensures thatthe effectiveness of the apparatus is predictable and thus reliable.

The UVC Radiation Generators radiating at 260 nm ensures that all theenergy is applied to the destruction of the DNA of the pathogens, thisattribute being an essential part of this disclosure.

What is claimed is:
 1. An apparatus for killing airborne pathogens in anairflow comprising: an air duct; at least one solid state UVC sourcemounted to a wall of said air duct for generating UVC light in saidduct; wherein the UVC source is configured to generate sufficient UVC insaid air duct to kill said pathogens, and is in communication with saidair duct and produces no ozone in said air duct.
 2. The apparatus asdefined in claim 1, wherein the air duct is reflective to UVC light. 3.The apparatus as defined in claim 1, wherein said UVC source produces awide angle beam in said duct.
 4. The apparatus as defined in claim 3,wherein the air duct is reflective to UVC light.
 5. The apparatus asdefined in claim 4, wherein two said UVC sources are opposed to oneanother in said duct.